Certain inertial reference systems, such as those associated with aircraft navigation, for example, require the inertial sensors (e.g., gyroscopes, accelerometers, etc.) to be mechanically isolated from the rest of the system in order to attain the required inertial sensor accuracy and reliability. Referring to FIG. 1, for example, an inertial-sensor assembly (ISA) 10 may be mounted within an enclosure or chassis 20 and vibration isolated from the chassis through the use of, for example, elastomeric isolators 30 operable to reduce sensor vibration exposure.
However, such an isolation scheme allows the ISA 10 to rotate through an angle 40 relative to the chassis 20 and, as such, the vehicle for which accurate spatial-orientation information is required. This may be due to a number of factors such as temperature, linear and angular acceleration, age, etc. Although, for purposes of clarity, rotation of the ISA 10 in a one-dimensional plane is shown in the drawing figures, the ISA is free to rotate slightly in all three dimensions. In conventional strapdown inertial navigation system arrangements, this rotational motion of the ISA 10 is generally unmeasured or otherwise unaccounted for in the inertial navigation solution calculated by a processing device 50 in signal communication with the ISA. Further, this motion degrades the knowledge of the chassis 20 orientation, even if the ISA 10 orientation is perfectly known.
As such, a mechanical isolation may itself be a source of misalignment error. Moreover, a typical navigation system does not, with great accuracy, take into account mechanical misalignment between the system chassis and the mechanically isolated ISA.